Diamine-curable polyurethane compositions

ABSTRACT

Diamine cured polyurethane compositions having unusually long pot life while rapidly curing at elevated temperatures and having remarkable storage stability at -40* F. are prepared by combining a prepolymer of a di or poly isocyanate and a hydroxy terminated polyether or polyester having a molecular weight in the 150 to 3,000 range, said prepolymer containing about 2.5 to 10% by weight -NCO, with a lower alkylene bis anthranilic acid ester or a suspension of a lower alkylene bis anthranilic acid ester in an anhydrous diluent selected from the group consisting of plasticizers and co-curing glycols, the proportions of said prepolymer and hardener being such as to provide an NH2:NCO ratio of about 0.9:1 to 1.0:1, and oleic acid as a polyurethane catalyst. The prepolymer and hardener, if degassed to remove air and moisture, provide stable two-component resin systems having excellent shelf life. One component systems with exceptional storage stability are prepared by mixing the prepolymer and hardener, freezing the mixture at -40*F. and storing the resulting composition at -40* F.

United States Patent [191 Ryan [11] )E Re. 28,541

[ Reissued Sept. 2, 1975 DIAMlNE-CURABLE POLYURETHANE [22] Filed: Oct.15, 1973 [21] Appl. No.: 406,588

Related U.S. Patent Documents Reissue of:

[64] Patent No.: 3,629,168

Issued: Dec. 21, 1971 Appl. No.: 818,801 Filed: Apr. 23, 1963 [52] U.S.CL... 260/18 TN; 260/22 TN; 260/312 N; 260/75 NB; 260/75 NH; 260/775 AB;260/775 AM [5l} Int. Cl. COSG 18/16; C08G 18/32 [58] Field of Search260/18 TN, 75 NB, 77.5 AB, 260/75 NH, 77,5 AM, 22 TN, 31.2 N

[56] References Cited UNITED STATES PATENTS 2,955,056 10/1960 Knox117/98 3,004,939 10/1961 Varvaro.. 260/22 3,463,748 8/1969Scheibelhoffer 260/18 3,471,445 10/1969 Carr 260/75 NH 3,478,089 11/1969Ogurana et a1. 260/5012 OTHER PUBLICATIONS Saunders etal.-Polyurethanes-Part I. Interscience, New York (1962) pp. 129-134,173-179.

Primary ExaminerI-I. S. Cockeram Attorney, Agent, or FirmHarris, Kern,Wallen & Tinsley [5 7] ABSTRACT Diamine cured polyurethane compositionshaving unusually long pot lifewhile rapidly curing at elevatedtemperatures and having remarkable storage stability at 40 F. areprepared by combining a prepolymer of a di or poly isocyanate and ahydroxy terminated polyether or polyester having a molecular weight inthe 150 to 3,000 range, said prepolymer containing about 2.5 to 10% byweight NCO, with a lower alkylene bis anthranilic acid ester or asuspension of a lower alkylene bis anthranilic acid ester in ananhydrous diluent selected from the group consisting of plasticizers andcocuring glycols, the proportions of said prepolymer and hardener beingsuch as to provide an NH :NCO ratio of about 0.921 to 1.0: 1 and oleicacid as a polyurethane catalyst. The prepolymer and hardener, ifdegassed to remove air and moisture, provide stable two-component resinsystems having excellent shelf life. One component systems withexceptional storage stability are prepared by mixing the prepolymer andhardener, freezing the mixture at 40F. and storing the resultingcomposition at 40 F.

12 Claims, No Drawings DIAMlNE-CURABLE POLYURETHANE COMPOSITIONS Matterenclosed in heavy brackets appears in the original patent but forms nopart of this reissue specification; matter printed in italics indicatesthe additions made by reissue.

BACKGROUND OF THE INVENTION In the preparation of strong, tough urethaneelastomers the best and most widely used amine type hardener heretoforeemployed has been 4,4methylene bisortho chloroaniline which is readilyavailable under the trademark MOCA. A limitation on its use, however,

has been its speed of reaction with most isocyanate pre-' polymers.Being a solid, it must be heated or dissolved in a solvent or veryfinely ground, and suitably dispersed in a carrier, to be convenientlydistributed throughout the prepolymer. Thorough mixing in the prepolymeris essential to give a strong, thoroughly cured elastomer, yet thereaction time when using MOCA is so rapid that proper mixing isfrequently difficult, and the pot life is too short for any but smalland simple castings without elaborate and expensive proportionating andmixing equipment.

ln US. Pat. No. 3,188,302 the preparation of polyurethane products usingMOCA as hardener is disclosed and claimed (claim In this patent it issignifi cant to note that in Example I this rapid reactivity of MOCA isrecognized in the statement casting quickly into molds. Furthermore, thestatement at column 7, lines to concerning the similar results obtainedon substitution of other amine hardeners for the MOCA is a clearindication that the patentee considered this rapid reactivity to becharacteristic of all the recited amine hardeners.

A further limitation on the MOCA systems. regardless of their pot life,has been their instability towards storage at reduced temperatures asone component, premixed or frozen" urethane. The MOCA systems are soreactive that even as low as 40 F. they cannot be stored for much longerthan two weeks without severe increases in viscosity and subsequent lossof pot life.

THE lNVENTlON It has now been discovered that it is possible to providepolyurethane systems having cured properties and characteristics similarto those obtained with MOCA as hardener, but having a pot life orworkable time 5 to 25 times longer than possible with MOCA. Pot life istaken as the time required to reach [00,000 cps. I: Mixed vis-] mixedvix-cosity for the 2 component systems and as the time required to reach200,000 cps. viscosity for the one component or frozen systems. Further,it is possible to provide systems which not only have longer pot lifebut which cure faster at room or elevated temperatures and which are 3to 20 times more stable towards storage at -40 F. than the conventionalMOCA cured urethanes by employing as hardener a loweralkylenebis-antliranilie acid ester. also known as a loweralkylene-bis-(Z-carboxyalkylaniline) of which methylene bis methylanthranilate (MMA) is the most readily available and preferred. It issignificant to note that this compound is actually referred to at column7. line 23 of US. Pat. No. 3,l88,3()2, as providing results similar tothose obtained with MOCA. This is so at variance with the discovery ofthe present invention that the statement should be disregarded as ameaningful disclosure.

in the new compositions of the present invention, a prepolymer of a dior poly isocyanate and a hydroxyterminated polyether or polyester havinga molecular Weight in the 150 to 3 ,000 range, said prepolymercontaining about 2.5 to 10% by weight-NCO, is combined with a loweralkylene bis anthranilic acid ester or a suspension of a lower alkylenebis anthranilic acid ester in an anhydrous diluent selected from thegroup consisting of plasticizers and co-curing glycols, the proportionsof said prepolymer and hardener being such as to provide a NH :NCO ratioof about 0.9:1 to 1.0:].

The isocyanates which can be employed are represented generally by theformula R( NCO) I where R is selected from the class consisting of diandpoly functional alkylene, arylene and aryl-alkylene groups containing 6to 14 carbon atoms and X is 2 to 4. Numerous isocyanates answering thisdescription are available and can be used in the composition with theselection of particular isocyanate depending in part on the physicalproperties desired in the cured composition. For good general purposeelastomers, the most widely used diisocyanate is toluene diisocyanate,particularly toluene 2,4-diisocyanate and commercial grade materialscontaining about to 2,4 and 35 to 20% 2,6 isomers. When harder andtougher elastomers are desired, and a somewhat higher cost is notobjectionable, it is customary to use 4,4-methylene bis-(phenylisocyanate) and commercial grades thereof which may include poly phenylmethylene polyisocyanates in which three or more phenyl isocyanategroups are combined by methylene groups. When products are desired whichare resistant to color change upon outdoor exposure, it is preferable toemploy lysine diisocyanate which is the methyl ester of hexanoic acid2,6-diisocyanate or other aliphatic diisocyanate.

Typical hydroxyterminated polyethers and polyesters for use in thepreopolymers include polypropylene glycols, polytetramethylene glycols,and polyesters which are reaction products of short glycols such asdiethylene glycol with dibasic acids.

Prepolymers of the type above described and the variations therein toachieve different properties in cured compositions are well-known to thepolyurethane art, and the novelty of the present invention resides notin the prepolymer, but rather in the particular type of diamine curingagent which so markedly prolongs the pot life or work time whilepermitting rapid curing at elevated temperatures, as well as giving longpremix storage life at low temperature, and providing properties in thecured product generally comparable to those obtained with other diaminecuring agents.

The superior diamine curing agents of the present invention may bedescribed as lower alkylene bis anthranilic acid esters in which thealkylene group and the ester groups may contain 1 to 3 carbon atoms.Most readily available, and hence preferred, of these anthranilic acidesters is methylene his methyl anthranilate MMA).

The anthranilie acid esters are solids which in a finely divided formare uniformly distributed throughout the prepolymer or the anthranilicacid esters are dispersed in a liquid diluent which has the property ofacting as a plasticizer or a eo-curing component for the polyurethanesystems. Glycols, for example, can be employed as well as phthalic acidesters such as dioctyl phthalate. Such dispersions can suitably containas much as 65% by weight of the anthranilic acid ester and suitablycontain a small amount of pigment such as carbon black, titanium dioxideor the like, both to provide the desired color in the end product and toprovide a colorimetric indicator of the uniformity of blending ofanthranilic acid ester with the prepolymer.

The anthranilic acid ester and prepolymer are preferably employed inproportions to provide an NHgNCO ratio of about 0.9:] to 1.0:1.

The anthranilic acid ester or suspension is blended with the prepolymerat room temperature or about 25C. At this temperature the blend willhave a pot life of the order of 3 hours to 1 1 hours or longer dependingupon the reactivity; i.e., the NCO content of the prepolymer. In someinstances, where the prepolymer may be too viscous to permit mixing atroom temperature, the temperature can be elevated slightly to reduce theviscosity. Any such elevation of temperature, however, should bemaintained at a minimum as this will tend to shorten the pot life oruseful working time of the blend.

It is also possible in the new systems to employ amounts on the order of1 to 3% based on the weight of the anthranilic acid ester or suspensionof a polyurethane catalyst such as oleic acid. [This has little effecton the pot life, but substantially reduces the cure time at both roomtemperature and elevated temperatures. I The polyurethane catalystreduces the long pot life and cure time attained by the use of thediamine hardeners of the present invention, at bat/z room temperatureand elevated temperature.

In making the new systems, the prepolymer and the anthranilic acid estersuspensions. with or without cata lyst, are preferably degassed toremove entrapped air and moisture and packaged in separate containers.Thus packaged, they exhibit very good shelf or storage stability withlittle change in the pot life and cure characteristics even after manymonths of storage. Alternatively the anthranilic acid ester may bedispersed directly into the prepolymer and the resulting compositionfrozen and stored at 40 F.

The following examples show the preparation of typical compositions inaccordance with the present invention in comparison with similarcompositions containing 4,4'-methylene bis-ortho chloroaniline (MOCA) asthe diarnine curing agent. It is to be understood, however, that theseexamples are given by way of illustration and not of limitation.

EXAMPLE I Dried methylene bis methyl anthranilate (MMA) and methylenebis-ortho chloroaniline (MOCA) were pow dered to pass a 200 mesh screen.The two powdered hardeners were mixed at 25 C. with prepolymers of l ,4polybutylene glycol and toluene diisocyanatc having -NCO concentrationsindicated in the following tabulation in proportions to provide an NHzNCO ratio of 0.9 to 1.0. Approximately 150 gram quantities of theresulting mixtures were observed for pot life at 25C. and 100C. with thefollowing results:

Pot Life at 25 C.

MMA MOCA Polymer A 4.127! NCO 10.5 hrs. 2 hrs. Polymer B 9.45% NCO 3.5-4hrs. 23 min.

Pot life at 100 C.

Polymer A 11.5 min. 18.2 min.

Polymer B is too reactive to use at 100 C. with either hardener. Notethat the new hardener, although very slow at 25 C., is more rapid thanMOCA at 100 C.

EXAMPLE ll 3 bis ortho chloroaniline, MOCA, providing a paste very muchlike that made with the MMA using parts of MOCA, 1 part of carbon blackand 66.7 parts of dioctyl phthalate. t

1,4 polybutylene glycol, toluene diisocyanate prepolymers similar tothose used in Example I but containing slightly different NCO content asindicated in the tabulation were mixed with the dispersions inproportions providing an Nl-l zNCO ratio of 0.95 to 1.0. To additionalquantities of the prepolymer-MMA hardener mixtures were addedapproximately 2% by weight of technical grade oleic acid as catalyst.The pot life for these mixtures at 25 C, is tabulated below.

Pot life at 25 C.

MMA. MMA plus MOCA, hrs. oleic, hrs. min.

Polymer C 7.7% NCO 4-5 2 25 Polymer D 9.08% 4.5 2 20 The roomtemperature curing rates of the three sam ples from polymer C werefollowed by noting the changes in hardness:

Shore D Values The catalyzed MMA system cures about as quickly as doesthe MOCA system, but yet shows a much longer working life. This isperhaps better illustrated by the viscosity build'up. Brookfield RVFviscosity, Spindle 7/20 r.p.m. g. mass at 250 C.:

POLYMER C VISCOSITY MMA plus catalyst.

Curing agent cps. MOCA.

cps.

minutes 1 1,000 13,400 minutes 11,000 15,000 30 minutes 13,600 31,000 43minutes 90,000 45 minutes 17,000 60 minutes 22,000

A comparison of the physical properties of resin systems cured 16 daysat room temperature with the MMA hardener plus catalyst and with theMOCA hardener are tabulated below:

EXAMPLE III A 1,4 polybutylene glycol, toluene, diisocyanate prepolymersimilar to those used in Examples 1 and II but having an excess NCO of6.3% was intimately mixed at C. with: (l) MMA powdered to pass a200 meshscreen, (2) MMA powder plus 2% by weight, on the prepolymer-hardenerblend, of technical grade oleic acid, (3) MOCA powdered to pass a 200mesh screen; such that the NH /NCO ratio was 0.9/1 to 1.0/ 1. Eachmixture was de-aired briefly to remove entrapped air and then pouredinto several tubular polyethylene containers. The temperature of eachcontainer was rapidly lowered to 40 F. by immersion in a DryIce-methanol bath and the containers were stored at 40 F. The

containers were then periodically removed from storage and rapidlywarmed until an average temperature of 25 C. was reached. The pot lives(time required to reach 200,000 cps.) were recorded as a function ofstorage time. The MOCA mixture lost 5 minutes of pot life for every 3days of storage time, the MMA mixture did not lose any pot life onstorage for over 90 days, and the MMA mixture plus 2% oleic acid lost 5minutes of pot life for every 9 days of storage. Not only were thestorage stabilities of the MMA and MMA-l-oleic acid mixture much greaterthan the MOCA mixture but their pot lives at 25 C. were greater. Theinitial pot life for the MMA mixture was 3 /2 hours, and MMA+oleic acidmixture had a 50 minute pot life while the MOCA blend had only 15minutes.

The room temperature cure times of the mixtures were measured byrecording the increase in Shore D hardness after 10 seconds indentationover a period of days. The results are tabulated below:

Shore D Values MMA plus MMA olcic MOCA 1 day 15 I0 2 days 10 32 25 3days 1 7 40 30 4 days 25 43 35 5 days 35 43 37 6 days 43 43 43 It shouldbe noted that the MMA-l-oleic even at room temperature cures about 2times as fast, has about 3 times the room temperature pot life and therate of viscosity drift versus storage at 40 F. is 3 times better thanthe MOCA system.

EXAMPLE IV A polypropylene glycol prepolymer is prepared by rapidlyadding 25 parts of toluene diisocyanate (80/20 mixture of the 2,4 and2,6 isomers) to an agitated sample of parts of a polypropylene glycol of1,500 molecular weight. The mix was warmed to 60, under nitrogen, andheld at that temperature for an hour. Then heat was removed, batchsealed up and allowed to stand overnight. This gave a prepolymer of6.15%

NCO.

It was cured with dispersions of MOCA and MMA in dioctyl phthalateprepared as describd in Example 11. The MMA dispersion was modified bythe addition of 2% oleic acid, which speeds its action. Hardeners werein proportion to provide an NH :NCO ratio of 0.9 to

At 25 C., the mixture containing MMA hardener and catalyst had a potlife of four hours, whereas the mixture containing MOCA hardener had apot life of only 45 minutes.

After cure for 16 hours at 150 F. plus 24 hours at room temperature (25C.), the products showed the following physical properties.

Physical Properties A polyester was prepared by combining three mols ofadipic acid and four mols of diethylene glycol. 0.1% stannous octoatewas used as catalyst and 5% toluene Was added to assist in the waterremoval. After 6 hours of gentle reflux the acid number was less thanone. The remaining toluene was taken off. The hot polyester (115 C.) wasvery fluid. It was cooled to 50 C. at which temperature it remainedfluid. 2.2 mols of technical p,p' diphenyl methane diisocyanate wasmelted and added at 50 C. to the hot prepolymer. There was a noticeableexotherm but by the use a cold water bath the temperature was held at C.Reaction subsided within a half hour and temperature started to fall.External heat was then applied and 80 temperature maintained for anotherhour. Cooled to room temperature, product a waxy solid, NCO content6.7%.

One hundred grams of the prepolymer was heated to 60 C. to make itreasonably fluid and 55.4 grams of an MMA dispersion in dioctylphthalate prepared as described in Example ll, was mixed in well. Potlife at this temperature was about 20 minutes, sufficient to permitde-airing and casting of a 12 inches X 12 inches X /8 inch sheet mold.The cast material gelled in 1 minutes at 125 C.

When fully cured, the cast elastomer showed the following physicalproperties:

Tensile strength-3,35O p.s.i. Elongation-328% ASTM D624 Die C Tear-475p.l.i. ASTM D470 Tear-l l6 p.l.i. Hardness, Shore D45-40 The sameprepolymer at 60 C. was mixed with a MOCA dispersion in dioctylphthalate (34.6 grams). The mixture exothermed somewhat, and gelled inless than a minute at the temperature reached, which was approximately75 C. This reaction was too fast to permit thorough mixing or de-airingand no casting could be made.

The foregoing examples demonstrate that the new MMA hardener provides apot life or working time at least five times longer and sometimes asmuch as 25 times longer than the pot life when using MOCA hardener atroom temperature. They also demonstrate that the increased pot life wasnot gained at the expense of cure time and indeed that systems can bedeveloped with MMA which will cure, even at room temperature, fasterthan the existing MOCA system and that these materials are from 3-20times more stable towards premix Storage at 40 F. than the eXiSting MOCAsystems.

Various changes and modifications in the polyurethane compositionsherein described and providing the unusually long pot life or workingtime may occur to those skilled in the art, and to the extent that suchchanges and modifications are embraced by the appended claims, it is tobe understood that they constitue part of the present invention.

I claim:

1. A heat curable polyurethane composition consisting essentially of aprepolymer of an organic diisocyanate and a hydroxy terminated polyetheror polyester having a molecular weight of from about 150 to 30,000, saidprepolymer containing from about 2.5 to 10% by weight -NCO; a diaminehardener for said polyurethane composition selected from the groupconsisting of lower alkylene bis anthranilic acid esters and suspensionscontaining up to about 65% by weight thereof in an anhydrous diluentselected from the group consisting of plasticizers and co-curingglycols, said prepolymer and hardener being present in an amount toprovide a ratio of NH zNCO of from about 0.9:1 to 1:1; and from about 1to 3% by weight of oleic acid as a polyurethane catalyst, saidpolyurethane composition being characterized in that it exhibitsprolonged, improved pot life at room temperature of at least about 3hours which is at least five times longer than the pot life of identicalpolyurethane compositions using 4,4 '-metlzylene bis-ortho chloroanilineas a hardener compared to lower alkylene bis anthranilic acid esterhardeners.

2. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from toluene diisocyanate.

3. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from commercial grade toluene diisocyanatecomprising at least of the 2,4 isomer.

4. A polyurethane composition as defined in claim 1 wherein theprepolymer is formed from 4,4'-methylene bis-( phenyl isocyanate 5. Apolyurethane composition as defined in claim 1 wherein the prepolymer isformed from the methyl ester of 2,6diisocyanato-caproic acid.

6. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from polypropylene glycol.

7. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from a polybutylene glycol.

8. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from a hydroxyterminated glycol dicarboxylic acidester.

9. A heat curable polyurethane composition consisting essentially ofpolyurethane prepolymers containing from about 2.5 to 10% by weight NCO,and a diamine hardener for said polyurethane composition consisting of alower alkylene bis anthranilic acid ester. said prepolymer and hardenerbeing present in an amount to provide a ratio of NH :NC() offrom about0.9:] to 1.1; andfrom about 1 to about 3% by weight of a polyurethanecatalyst, said polyurethane composition being characterized in that itexhibits prolonged, improved pot life, which is at least five timeslonger than the pot life of identical polyurethane compositions using 4,4'-methylene bisortlzo chloroaniline as a hardener compared to loweralkylene bis anthranilic acid ester hardeners.

10. A heat curable polyurethane composition as set forth in claim 9wherein said polyurethane catalyst is oleic acid.

II. A heat curable polyurethane composition as set forth in claim 9wherein said polyurethane catalyst is stannous octoute.

12. A heat curable polyurethane composition as set fort/1 in claim 9wherein said ltardener is methylene bis methyl anthranilatc.

1. A HEAT CURABLE POLYURETHANE COMPOSITION CONSISTING ESSENTIALLY OF APREPOLYMER OF AN ORGANIC DIISOCYANATE AND A HYDROXY TERMINATED POLYETHEROR POLYESTER HAVING A MOLECULAR WEEGHT OF FROM ABOUT 150 TO 30,000, SAIDPREPOLYMER CONTAINING FORM ABOUT 2.5 TO 10% BY WEIGHT - NCO, A DIAMINEHARDENER FOR SAID POLYURETHANE COMPOSITION SELECTED FROM THE GROUPCONSISTING LOWER ALKYLENE BIS ANTHRANILIC ACID ESTERS AND SUSPENSIONSCONTAINING UP TO ABOUT 65% BY WEIGHT THEREOF IN AN ANHYDROUS DILUENTSELECTED FROM THE GROUP CONSISTING OF PLASTICEZERS AND CO-CURING GYCOLS,SAID PREPOLYMER AND HARDENER BEING PRESENT IN AN AMOUNT TO PROVIDE ARATIO OF NH2:NCO OF FROM ABOUT 0.9:1 TO 1:1: AND FROM ABOUT 1 TO 3% BYWEIGHT OF OLEIC ACID AS A POLYURETHANE CATALYST, SAID POLYURETHANECOMPOSITION BEING CHARACTERIZED IN THAT IT EXHIBITS PROLONGED, IMPROVEDPOT LIFE AT A ROOM TEMPERATURE OF AT LEAST ABOUT 3 HOURS, WHICH IS ATLEAST FIVE TIMES LONGER THAN THE POT LIFE OF IDENTICAL POLYURETHANECOMPOSITIONS USING 4,4''-METHYLENE BIS-ORTHO CHLOROANILINE AS A HARDENERCOMPARED TO LOWER ALKYLENE BIS ANTHRANILIC ACID ESTER HARDENERS.
 2. Apolyurethane composition as defined in claim 1 wherein said prepolymeris formed from toluene diisocyanate.
 3. A polyurethane composition asdefined in claim 1 wherein said prepolymer is formed from commercialgrade toluene diisocyanate comprising at least 65% of the 2,4 isomer. 4.A polyurethane composition as defined in claim 1 wherein the prepolymeris formed from 4,4''-methylene bis-(phenyl isocyanate).
 5. Apolyurethane composition as defined in claim 1 wherein the prepolymer isformed from the methyl ester of 2,6-diisocyanato-caproic acid.
 6. Apolyurethane composition as defined in claim 1 wherein said prepolymeris formed from polypropylene glycol.
 7. A polyurethane composition asdefined in claim 1 wherein said prepolymer is formed from a polybutyleneglycol.
 8. A polyurethane composition as defined in claim 1 wherein saidprepolymer is formed from a hydroxyterminated glycol dicarboxylic acidester.
 9. A heat curable polyurethane composition consisting essentiallyof polyurethane prepolymers containing from about 2.5 to 10% by weightNCO, and a diamine hardener for said polyurethane composition consistingof a lower alkylene bis anthranilic acid ester, said prepolymer andhardener being present in an amount to provide a ratio of NH2:NCO offrom about 0.9:1 to 1.1; and from about 1 to about 3% by weight of apolyurethane catalyst, said polyurethane composition being characterizedin that it exhibits prolonged, improved pot life, which is at least fivetimes longer than the pot life of identical polyurethane compositionsusing 4,4''-methylene bis-ortho chloroaniline as a hardener compared tolower alkylene bis anthranilic acid ester hardeners.
 10. A heat curablepolyurethane composition as set forth in claim 9 wherein saidpolyurethane catalyst is oleic acid.
 11. A heat curable polyurethanecomposition as set forth in claim 9 wherein said polyurethane catalystis stannous octoate.
 12. A heat curable polyurethane composition as setforth in claim 9 wherein said hardener is methylene bis methylanthranilate.